Recently there has been a demand for the ability to receive mobile communication services of different frequency bands through one mobile communication terminal, even as mobile communication terminals become smaller and lighter. There is a demand for terminals that are able to use signals of multiple bands simultaneously as necessary, for mobile communication services using a variety of frequency bands such as, for example, the CDMA service of the 824-894 MHz band and the PCS service of the 1750-1870 MHz, which have been commercialized in Korea, the CDMA service of the 832-925 MHz band, which has been commercialized in Japan, the PCS service of the 1850-1990 MHz band, which has been commercialized in the U.S., the GSM service of the 880-960 MHz band, which has been commercialized in Europe and China, and the DCS service of the 1710-1880 MHz band, which has been commercialized in parts of Europe; for accommodating such multiple bands there is a demand for an antenna having wide band characteristics.
Besides these, there is also a demand for composite terminals that are able to use services such as Bluetooth, ZigBee, wireless LAN, GPS, etc. In such a terminal for using services of multiple bands, a multiple band antenna should be used that is able to operate in two or more bands. For an antenna of a generally used mobile communication terminal, a helical antenna and a planar inverted-F antenna (PIFA) are mainly used.
Here, a helical antenna is an external antenna affixed to the top end of a terminal, and is used together with a monopole antenna. A helical and monopole antenna in combined usage is such that if the antenna is extended out of the body of the terminal, it acts as a monopole antenna, and if it is retracted, it acts as a λ/4 helical antenna. Such an antenna has the advantage of high profits, but due to its non-directivity, the SAR (specific absorption rate)—the standard for the level of harmfulness of electromagnetic waves to the human body—is not good. Also, as a helical antenna is constructed as protruding out of a terminal, it is not easy to provide an esthetic appearance and an external design suitable to portability of the terminal, and no study has been done on an internal structure with regards to this.
An inverted-F antenna is an antenna designed with a low profile structure for the purpose of overcoming such disadvantages. An inverted-F antenna has a directivity that improves its SAR by reducing the beams emitted towards the human body, left over from the beams going toward the ground, out of all the beams generated by the current left in the radiating part, while at the same time strengthening the beams left to go in the direction of the radiating part; and it may also be implemented as a low profile structure operating with a square micro-strip antenna, the length of the rectangular flat-board radiating part being reduced in half.
Since such an inverted-F antenna has radiating characteristics with a directivity that reduces the strength of beams going toward the human body and fortifies the strength of the beams going outward from the body, it has a superior electromagnetic specific absorption rate when compared with a helical antenna. However, an inverted-F antenna has the problem of having a narrow frequency band width.
The narrow frequency band width of an inverted-F antenna is due to point-matching, in which the matching with a radiator takes place at a specific point.
In order to overcome the problem related to a narrow band width due to point matching, an application was submitted for a Korean patent by the inventor, and this application presents a structure that overcomes the problem of a narrow band width of the existing inverted-F antenna by means of coupling matching and coupling feeding in a comparatively long interval.
However, there was the problem of the size of the antenna being large, as a separate impedance matching part for such coupling matching and coupling feeding occupied a comparatively large space.